Art of transferring preformed films to various bases



Patented Nov. 5, 1940 UNITED STATES ART OF TRANSFERRING .PREFORM'EDFIIMS TO VARIOUS BASES Milton 0. Schur and Benjamin G. Hoos, Berlin,

N. H., assignors to Brown Company, Berlin, N. H., a corporation of MaineNo Drawing. Application June 10, 1937, Serial No. 147,490

2 Claims.

This invention relates to the art of transferring preformed films tovarious bases and deals more specifically with preformed films ofmaterials capable of being gelled by or dissolved in volatile organicsolvents. While the method hereof might be applied in transferringpreformed films to various bases, including leather and many kinds offabric, it is particularly useful in providing an artificial. leatherconsisting essentially of a rubber-impregnated felt base with a smoothand attractive wear layer or surface simulating in appearance andapproximating in moisture-proofness, scuff-resistance, handle or feel,and other physical properties, the grain or enamel side of such naturalleather as calfskin. In this connection, it should be noted that thetransferred film must be of extreme thinness or light weight and yet befree from even minute blemishes or imperfections especially whentransferred to a rubber-impregnated felt base to serve in lieu ofnatural calfskin or the like for such exacting purpose as making ladieshandbags.

Inasmuch as the film-forming materials used for the purposes hereof aresoluble in volatile organic solvents but include materials falling intosuch different chemical categories as cellulose esters (e. g.nitrocellulose), cellulose ethers (e. g. ethyl cellulose), andartificial resins, (e. g. vinyl resins), we shall for convenience ofdesignation hereinafter use the term lacquer as applied to all of suchmaterials. Indeed, organic solvent solutions of such materials, fromwhich the films hereof are prepared, are common called lacquers byreason of their usefulness in depositing so-calIed lacquer films onvarious surfaces to be protected against weathering or wearinginfluences and/or to present a finished or. ornamental appearance.

The transfer of a lacquer film to a rubber-impregnated felt base is byno means a simple problem when the film-weight is low, say, less than 20grams per square foot, and when the transferred film must additionallybe free from imperfections and yet be made to adhere tenaciously to suchbase. When one stops to consider also that tenacious adherence of thetransferred film to such base can be had only by pressing the film whilein solvent-activated condition against such base, that is, while thefilm is especially susceptible to marring or crushing, he realizes atonce some of the troublesome aspects of the problem.

After considerable work on the foregoing problem, we have found itadvantageous to preform the lacquer film on a smooth metal plate or itsequivalent; to activate the film, preferably while still on the plate,with alacquer solvent admixed with a large amount of non-solvent,preferably a preponderant amount of the non-solvent; to press thesolvent-activated film, preferably plate and all, against the rubberimpregnated felt base; to dry, preferably air-dry, the film thus pressedagainst the base; and finally to strip the base from the plate,preferably after exposure of the pressed-together layers to anatmosphere of warm air saturated with water vapor. By properlyperforming such a method, we have found that not only is a transfer ofthe lacquer film to the base accomplished but that the transferred filmis to all intents and purposes free from surface imperfections and isvery tenaciously adherent to the base.

In carrying out the method hereof, the lacquer film may be preformed bythinly applying a lacquer solution in any suitable way on a smooth metalplate, for instance, a stainless steel plate, and then drying theapplied lacquer under suitable temperature conditions. Specifically, theusual nitrocellulose lacquers of commerce may be employed; and they maybe of such controlled solids content and viscosity or fluency that amomentary dipping of the metal plate thereinto will leave, afterdrainage of the excess lacquer from thedipped plate maintained insubstantially vertical position, a lacquer film or deposit oi thedesired thickness or weight and-smoothness. If desired, the lacquers maybe sprayed, painted, or otherwise applied as a substantially uniformfilm of the appropriate thinness on the metal plate. The lacquer film isthen dried on the metal plate, preferably under temperature conditionsbelow the boiling point of such volatile solvents as may be present inthe lacquer solution, thereby avoiding pin holes or other imperfectionsin the film.

The activation of the lacquer film after having thus been dried againstthe metal plate is preferably effected by dipping the plate into anactivating bath under conditions designed to develop the requisiteadhesiveness on the exposed film face to be pressed against therubber-impregnated felt base. While various factors, includingthetemperature of the activating bath, the length of time the film iskept therein, and the pressure exerted when the activated film is laidon the base, should be carefully controlled for the securement' of theresults desired herein, the most important single factor is perhaps thecomposition of the activating liquid; and such com-- position depends,among other considerations, upon the thickness of the lacquer film, uponthe porosity of the base to which its transfer is to be effected, uponthe pressure exerted in transferring the film to the base, etc. Atypical activating bath, which has been found to give consistentlyexcellent results with nitrocellulose films weighing about 6 to 8 gramsper square foot, is composed by weight of 5 parts of ethyl acetate, 5parts of cellosolve acetate, and 90 parts of 95% ethyl alcoliol. Itmight be noted that the ethyl alcohol is the inactive or non-solventingredient in such bath. With heavier film it becomes necessary toincrease the proportions of ethyl acetate and/or cellosolve acetate inthe activating bath, other factors being maintained constant. Thetrade-mark cellosolve designates an organic liquid solvent whosechemical name is ethylene glycol mono-ethyl ether. Cellosolve" acetateis simply the acetate of such ether.

As to the pressure exerted during the transfer of the activated film tothe rubber-impregnated felt base, it is to be observed that, althoughheavy pressure tends to improve the tenacity with which the film adheresto the base,

yet the activated film may be marred or crushed under unduly heavypressure, especially when the film weight is low and when the base is ofcomparatively rough texture and/or high porosity. Since therubber-impregnated felt bases designed to carry the transferred filmhereof desirably consist of highly absorptive webs of interfeltedcellulose fibers, for instance, refined wood pulp fibers of high alphacellulose content, and are impregnated with rubber very considerablyshort of complete saturation or filling of their pores or voids, thepressure exerted in laying the activated film on such bases should becarefully controlled to be well below that inlurious to the film. Fornitrocellulose films that weigh about 6 to 8 grams per square foot andthat are to be transferred to a rubber-impregnated felt of the characterjust described, the activating solution or bath may advantageously becomposed by weight of 15 parts of cellosolve" acetate, 7.5 parts ofethyl acetate, and 77.5- parts of toluol. The inactive or non-solventingredient in such bath is the toluol. It has been found that suchactivating bath possessed the important advantage over that previouslydescribed in that it makes for greater tolerance in the range ofpressures applicable to the activated film as it is being laid onto therubber-impregnated felt base while avoiding injury to the film.

Once the activated film and the smooth metal plate backing therefor havebeen pressed and dried against the rubber-impregnated artificial leatherbase, such film evidently has vastly greater grip or hold on the basethan on the metal plate.

"It is hence not surprising that the base can be stripped or removedwith the film cleanly transferred thereto from the metal plate,especially when stripping is facilitated by exposing the superposedlayers or plies for a short period, say, about a half hour, in anatmosphere of warm air saturated with water vapor, which atmosphereprobably diffuses in between the film and plate surfaces and thusweakens the already comparatively weak bond or hold of the film on thesmooth plate surface.

It is well to note the particular kind of adhesive activation effectedon the preformed lacquer films hereof, that is, the condition of theactivated films after they have been steeped or soaked in the activatingvolatile organic liquid media employed for the purposes hereof. In thisconnection, it should be observed that such activating media causeactual gelling of the lacquer films and that the films are applied tothe receiving bases in such gelled condition. To show that the lacquerfilms hereof are actually gelled before they are applied to thereceiving bases, we submerged strips of preformed nitrocellulose filmafter they had been removed from the forming background in theactivating baths hereinbefore described, namely a bath in which alcoholserved as the inactive ingredient and in a bath in which toluol servedas the inactive ingredient. For purposes of comparison we also putstrips of the preformed film into ordinary so-called thinner fornitrocellulose lacquer. In the case of the activating liquid mediahereof, the strips of nitrocellulose film were intact even after theyhad been in contact with such media for one-half hour and longer anddespite the fact that the containing vessels were mildly shaken duringthis period. In the case of the lacquer thinner, on the other hand, thestrips of nitrocellulose film began to dissolve in a few seconds andthey were badly disintegrated within a minute. When the strips ofnitro-cellulose film after exposure to the activating liquid mediahereof were rubbed with a stirring rod, they were found to be very slimyand to have the appearance and other earmarks of being swollen andgelled. It is thus seen that the activating or conditioning liquid mediahereof are truly swelling and/or gelling agents for the preformedlacquer films rather than powerful solvents of such films. While theactivating or conditioning liqiuid media hereof may act as solvents forthe preformed lacquer films under some conditions of use, for instance,if heated and/or if kept in contact with such films for a sufficientlylong time and/or if vigorously agitated, yet they are used pursuant tothe invention hereof under conditions such that they swell and/orgelatinize such films while such films are maintained intact andsubstantially undissolvedf Accordingly, the activating liquid mediahereof may well comprehend single volatile organic liquids incontradistinction to the mixtures of such liquids hereinbeforedescribed.

Although the invention hereof has been described more particularly inconnection with the transfer of preformed lacquer films to an artificialleather base consisting essentially of rubber-impregnated waterlaidfelt, it may be applied also in transferring such films to porousfibrous bases generally and to fibrous bases impregnated with bindersother than rubber. When a binder-impregnated waterlaid felt base iscoated with lacquer, as opposed. to being provided with a transferredlacquer film by the invention hereof, the uneven texture or internalstructure of such base will show through the coating when the weight ofthe coating or film is less than about 20 grams per square foot,especially when such base is unembossed. The undesirable revelation or"show-through of the uneven texture or surface irregularities in animpregnated waterlaid felt base is especially noticeable when the basecontains more than about 25% binder, based on the Weight of fiber, andis possessed of substantial residual porosity. Despite the fact that thetransferred lacquer films hereof are of a weight not exceeding about 20grams per square foot and despite the fact that the artificial leatherbases to which they are transferred by the invention hereof may consistof rubber-impregnated waterlaid felts containing distinctly more than25% rubber, based on the weight of fiber, and possessed of substantialresidual porosity, such transferred lacquer films besides beingtenaciously adherent to such artificial leather bases and being freefrom blemishes serve the highly desirable purpose of completely maskingthe uneven .tex ture or internal structure of such base.

Artificial leathers to which films have been transferred by the methodhereof may be used in various fields in lieu of such natural leather ascalfskin. For instance, they have proven acceptable to manufacturers ofbetter grades of ladies handbags; and handbags made from the finishedartificial leathers hereof are now available on the market with thedesignation that they are made from Solkalf, which quoted term is thetrade-mark for such artificial leathers. The lacquer films transferredby the methods hereof may, of course, present such color as may bedesired by adding pigment and/or dye of the appropriate color and inappropriate amount to the lacquer from which such films are formed. Itis to be understood that the foregoing examples of the method hereof aresubject to considerable variation as regards the temperature andcomposition of the activating bath, the length of time the preformedfilm is kept in the bath, the pressure applied when the activated filmis laid on the base, the particular kind of lacquer film beingtransferred, the particular base to which transfer of the film iseffected, the extent to which the activated film is dried against thebase before the base is stripped with the film transferred thereto fromthe smooth metal plate or its equivalent, etc. while still fallingwithin the purview of the present invention as defined by the appendedclaims. Again, it is to be understood that adhesive substances such asshellac, resins, or the like may be added to the activating medium orbath hereof without departing from the spirit or scope of the instantinvention. In such case, too, it is necessary that the activating mediumor bath swell and gell the film properly, for it has been found that theuse of cementing substances in such medium does not makefor the desiredtenacity of bond between the lacquer film and the base to which it istransferred unless the film itself has been adhesively activated to theproper extent, that is, has been transformed to a swollen and gelledcondition. While a smooth metal plate has been described as the smoothbackground for preforming the lacquer films hereof, since such a platemay be conveniently and economically handled in actual practice, itshould be understood that other smooth backgrounds might be used forpreforming such films and that;

the expression smooth background as used in the appended claims is meantto include various smooth backgrounds serviceable for preforming thefilms, for instance, metal, glass, porcelain, glazed papers, or the liketo which lacquer films adhere comparatively poorly; and it might also benoted that the background might be etched or embossed to impart thedesired grain to the film. It is not necessary that the background berigid or inflexible, since a flexible steel belt, transfer papers, etc.,might be used for preforming the lacquer films hereof.

-We claim:

1. A method of finishing a rubber-impregnated felt base witha lacquerfilm soluble in a volatile organic solvent, which comprises preformingsuch film on a smooth background'at a weight not exceeding about gramsper square foot, said background having much lower adhesive affinity forsaid film than said base, dipping the background carrying such lacquerfilm into a liquid bath containing a volatile organic solvent of saidlacquer and a volatile organic non-solvent of said lacquer to activateadhesively the surface of such film, pressing said activated film,background and all, against the surface of said rubber-impregnated feltbase, drying the film against said base surface, and stripping the basewith the film cleanly transferred thereto from said background.

2. A method of finishing a rubber-impregnated felt base of high residualporosity with a lacquer film soluble in a volatile organic solvent,which comprises preforming such film on a smooth background at a weightnot exceeding about 20 grams per square foot, said background havingmuch lower adhesive affinity for said film than said base, dipping thebackground carrying such base surface, exposing the superposed layers towarm moist air, and stripping the base with the film cleanly transferredthereto from said background.

MILTON O. SCHUR. BENJAMIN G.- HOOS.

